I tend to fall back on the belief that the power of crystals comes from their symbolic nature. Dreams are very strongly impacted by intention and belief, if you believe a certain crystal has a certain effect, then it will likely cause that effect to manifest. This can most certainly be used to your advantage as a means to manipulate and reinforce your intent. Whether or not the effect is ‘placebo’ or something more is pretty much irrelevant from my perspective. Crystals are things of beauty, nice to handle and have a practical use here too.
Given that mentality, then the meaning of the crystal to you, is what is most important. In choosing the right crystal, it’s best to think about what it means from your perspective. Of course reading what others assert as the meaning/power of the crystal is a good place to start. Then choosing one which best represents your intent. For example, some sites say calcite helps with memory, if you want to improve dream recall… it makes sense to use calcite to signify this. In this way if nothing else it becomes a physical representation of your will. Even in a purely scientific paradigm, it can’t be denied that can be powerful.